Sorption of Polycyclic Aromatic Compounds to Humic and Fulvic Acid HPLC Column Materials Katrin Kollist-Siigur, Torben Nielsen,* Christian Grøn, Poul Erik Hansen, Christian Helweg, Kristoffer E. N. Jonassen, Ole Jørgensen, and Uuve Kirso ABSTRACT dissolved humic matter, and soil or sediment humic mat- ter (Calvet, 1989; Schwarzenbach et al., 1993; Totsche Two different humic acids (HA) and a fulvic acid (FA) were chemi- et al., 1997). Binding of nonionic organic compounds to cally immobilized to a high performance liquid chromatography soils and sediments depends on the concentration of (HPLC) silica column material. The immobilization was performed by binding amino groups in HA/FA to the free aldehyde group in organic carbon (OC) in the solid (de Maagd et al., 1994; glutardialdehyde attached to the silica gel. The HPLC column materi- Means et al., 1980). The distribution coefficient, K oc (mol als were compared with a blank column material made by applying kg -1 OC/mol L -1 water), is a measure for the binding of the same procedure but without immobilizing HA or FA. Also, a the compound. Generally, a simple linear relationship column was made by binding carbonyl groups in HA to amino groups between binding and total OC of the solid is assumed, attached to the silica gel. The humic substances were selected to secure but recently, a dependency also upon the properties of appropriate variation of their structural features. The retention factors the solid organic matter has been demonstrated (Chiou of 45 polycyclic aromatic compounds (PAC) to the four columns were et al., 1998; Gauthier et al., 1987). Humic substances determined by HPLC. The advantage of the technique is a large constitute a large fraction of the solid organic matter in number of compounds can easily be studied. The binding procedure soils and sediments. The molecular size appears to be does not appear to cause a drastic selection between the HA mole- cules. The k values obtained for the two Aldrich HA columns agree an important factor determining the binding of solids in general reasonably. The retention or sorption of the compounds to organic matter (Chiou et al., 1986; Engebretson et increased with the size of the PAC and the number of lipophilic al., 1996; Engebretson and Wandruszka, 1997). Gauthier substituents, but decreased when polar substituents were present. The et al. (1987) found that K oc for pyrene binding to four PAC retention was much stronger to the two HA columns than to different humic acids increased from 0.9  10 5 to 2.0  the FA and blank column, both for hydrophobic polycyclic aromatic 10 5 L kg -1 as the humic acid aromatic fraction varied hydrocarbons (PAH) and the polar PAC. Other factors impacting from 0.20 to 0.34 of total C. One explanation for the the PAC binding may be specific interactions with HA and the ionic changes in binding with the properties of the solid or- strength of the aqueous phase. The technique has been applied to do ganic matter is that the binding may be either by adsorp- direct determinations of K oc . tion or by partitioning into the surface organic phase of the humic acids (LeBoeuf and Weber, 1997; Murphy et al., 1990). The process appears to shift from partitioning A mong the organic pollutants in the environment, to adsorption with the diagenetic alteration of the mate- the polycyclic aromatic compounds (PAC) have rials and thus with decreasing O/C and increasing H/C caused major concern because many are considered to elemental ratios (Huang and Weber, 1997). be carcinogenic (IARC, 1983). Besides, PAC with nitro- The complexity and inhomogenity of humic sub- gen atoms in the structure (N-PAC) have recently been stances precludes determination of their exact structures demonstrated to be phytotoxics (Gissel-Nielsen and for evaluation of the impact of their structural variability Nielsen, 1996). A number of different PAC has been upon the binding capacity for organic compounds. The identified in the environment. The best known group substances exhibit a great variation in their content of is the hydrophobic polycyclic aromatic hydrocarbons aromatic and aliphatic C, N, and S, and phenolic and (PAH), but also N-, S-, O-PAC, a number of different carboxylic acid groups (Aiken et al., 1996; Garcia et al., oxygenated derivatives, phenols, quinones, ketones, al- 1994; Gauthier et al., 1987; Malcolm and MacCarthy, dehydes and carboxylic acid derivatives, and nitro and 1986; Schulten, 1995; Wershaw, 1986). The inhomogen- chloro substituted PAC have been found (Blanco et al., ity of the humic samples is also reflected in their broad 1992; Haglund et al., 1987; Nielsen et al., 1983; Young- molecular weight distributions and also the chemical blood and Blumer, 1975). structures of the different molecular size fractions vary Transport, fate, and bioavailability of organic pollut- (Tanaka and Senoo, 1995). As an example, the fraction ants in the aquatic and terrestrial environment depend of aromatic C varied from 0.14 to 0.51 and the content on the partitioning of these compounds between water, of carboxylic C from 0.06 to 0.30 for humic substances isolated from Danish ground water systems (Grøn et K. Kollist-Siigur and U. Kirso, National Inst. of Chemical Physics and al., 1996). Biophysics, Akadeemia tee 23, EE-12618 Tallinn, Estonia; K. Kollist- Humic acid chemically bonded to HPLC column ma- Siigur, T. Nielsen, C. Grøn, C. Helweg, K.E.N. Jonassen, and O. Jørgensen, PBK 313, Risø National Lab., P.O. Box 49, DK-4000, Abbreviations: HA, humic acid; FA, fulvic acid; HPLC, high perfor- Roskilde, Denmark; and P.E. Hansen, Dep. of Life Sciences and mance liquid chromatography; PAC, polycyclic aromatic compounds; Chemistry, Roskilde Univ., P.O. Box 260, DK-4000, Roskilde, Den- PAH, polycyclic aromatic hydrocarbons; t r , retention time; t 0 , dead mark. Received 7 May 1999. *Corresponding author (torben.nielsen@ volume; k'= (t r - t 0 )/t 0 , capacity coefficient; OC, organic carbon; risoe.dk). K oc , organic carbon partition coefficient; K ow , octanol-water partition coefficient; NMR, nuclear magnetic resonance. Published in J. Environ. Qual. 30:526–537 (2001). 526 Published March, 2001